A converging slot hole is considered as a high-performance film hole with excellent film cooling effectiveness and relative lower aerodynamic loss. Previous studies on converging slot holes mainly focused on the film cooling effectiveness and heat transfer characteristics, whereas the discharge coefficient has not been fully studied, especially when the compressible effects cannot be ignored. In this study, we numerically evaluated the compressible effects on the discharge coefficient of converging slot hole and developed promising prediction methods for the discharge coefficient with both external and internal crossflows. Moreover, the effects of coolant direction relevant to the mainstream were also analyzed. The results show that the discharge coefficients and flow fields of converging slot hole were susceptible to the internal crossflow directions and compressible external/internal crossflows. Moreover, the additional loss caused by the external and internal crossflows was found to be independent of the loss inside the hole in certain cases. The empirical correlations for the discharge coefficient of converging slot hole based on the no crossflow data were found to be consistent with the numerical results, validating the numerical methods used in this study.